1. Field of the Invention
The present invention relates to a current providing circuit and a voltage providing circuit, and particularly relates to a current providing circuit and a voltage providing circuit, that have turn on/turn off time period based on the characteristic for the device therein and a voltage the device therein is coupled.
2. Description of the Prior Art
FIG. 1(a) is a circuit diagram illustrating a prior art voltage providing circuit 100. As shown in FIG. 1(a), the voltage providing circuit 100 is utilized to provide an output voltage V_cell_H to a memory array 102, to charge the bit line capacitors of the memory array 102. In one example, the output voltage V_cell_H is provided to 1st sense amplifiers of the memory array 102.
The voltage providing circuit 100 includes a regulator 101 and a current providing circuit 103 for suppressing voltage drop of the output voltage V_cell_H. The regulator 101, which includes an operational amplifier 105, a PMOSFET 107, and resistors 109, 111, is utilized to generate the output voltage V_cell_H. However, since the memory array 102 includes a lot of devices thus the output voltage V_cell_H may have a sudden drop due to charging for devices of the memory array 102 (ex. the bit line). Therefore, the current providing circuit 103, which has a PMOSFET 104 coupled to a voltage level Vccx, is provided to prevent the output voltage V_cell_H from dropping too much.
FIG. 1(b) is a schematic diagram illustrating the operation of the circuit shown in FIG. 1(a). As shown in FIG. 1(b), the output voltage V_cell_H drops when the regulator 101 turns on (the time period that the signal EN has a high voltage level). Simultaneously, the current providing circuit 103 also turns on (the time period that the signal XTR has a low voltage level, the PMOSFET 104 turns on), such that the output voltage V_cell_H can be raised up.
However, the time period for turning on the current providing circuit 103 is hard to be controlled. If the PMOSFET 104 turns on for a time period that is too long, the output voltage V_cell_H is raised too much. On the contrary, if the PMOSFET 104 turns on for a time period that is too short, the output voltage V_cell_H is too low. The performance of other devices may be affected due to incorrect output voltage V_cell_H. In the worst case, the devices may have no function, if the output voltage V cell H is too high or too low. Also, many parameters such as the value of Vccx, the characteristics for the PMOSFET in the current providing circuit, and the value of real time output voltage V_cell_H may affect the voltage raising speed of the current providing circuit 103. Also, the variation caused by environment parameters such as temperature, or the variation caused by the process for the bit line capacitors and the PMOSFET are different. Such that the controlling of the current providing circuit 103 is more complicated.
Therefore, a current providing circuit with better control mechanism is needed.